Fuel cell assembly and fuel cell system

ABSTRACT

A fuel cell assembly ( 1 ) is disclosed. The fuel cell assembly ( 1 ) has a fuel cell stack ( 2 ) formed by laminating a plurality of cells; plus and minus current extraction sections ( 4 ), the current extraction sections ( 4 ) extracting current generated by the fuel cell stack and sandwiching the fuel cell stack with respect to the direction of lamination; and a passage ( 4   a ) allowing flow of a fluid provided in at least one of the current extraction sections. Further a fuel cell system, which has the above fuel cell stack and a heating device ( 24, 26, 32, 90 ) for heating the passage for the fluid, is disclosed.

RELATED APPLICATION

This application is the U.S. National Phase under 35 U.S.C. § 371 ofInternational Application No. PCT/JP2004/003781, filed Mar. 19, 2004,which in turn claims the benefit of Japanese Application No.2003-123673, filed Apr. 28, 2003, the disclosures of which Applicationsare incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

This invention relates to a fuel cell assembly and a fuel cell system.

BACKGROUND OF THE INVENTION

During a cold startup of a fuel cell stack at a temperature belowfreezing, it is not possible to extract a desired power generationamount from the fuel cell stack because moisture which was previouslyproduced in the fuel cell during power generation freezes. Even if fuelgas is supplied to the fuel stack, since the reaction face (or membraneelectrode assembly) is covered with ice, it is impossible to supply thereaction face with a sufficient amount of fuel gas. U.S. Pat. No.6,358,638B1 and 6,103,410 disclose a technique for improving startup ofa cell fuel stack at a temperature below freezing. The techniquedisclosed in U.S. Pat. No. 6,358,638B1 melts ice using combustion heatproduced in a fuel cell by allowing a small amount of hydrogen or air toflow into the anode or the cathode. The technique disclosed in U.S. Pat.No. 6,103,410 promotes melting of ice in the fuel cell stack byintroducing a gaseous mixture of hydrogen gas and air into the cathodeand thus performing catalytic combustion of the gaseous mixture in thecathode.

SUMMARY OF THE INVENTION

However the conventional techniques above can be characterized in thatimmediately after startup, heat for heating the end cell positioned onboth ends of the fuel cell stack is used up as a result of heating theend plate or the current extraction plate positioned on both ends of thefuel cell stack. Consequently it is not possible to heat the end cellsufficiently. As a result, the power generation state of the end cell isconspicuously lower than other cells.

It is therefore an object of this invention to improve startup of theend cell in the fuel cell stack under cold conditions at a temperaturebelow freezing.

In order to achieve the above object, this invention provides a fuelcell assembly comprising a fuel cell stack formed by laminating aplurality of cells; plus and minus current extraction sections, thecurrent extraction sections extracting current generated by the fuelcell stack and sandwiching the fuel cell stack with respect to thedirection of lamination; and a passage allowing flow of a fluid providedin at least one of the current extraction sections.

Further, this invention provides a fuel cell system comprising the abovefuel cell assembly and a heating device for heating the passage for thefluid.

Furthermore, this invention provides a fuel cell assembly comprising afuel cell stack formed by laminating a plurality of cells; plus andminus current extraction sections, the current extraction sectionsextracting current generated by the fuel cell stack and sandwiching thefuel cell stack with respect to the direction of lamination; and anenclosed cavity for confining fluid therein formed in at least one ofthe current extraction sections.

The details as well as other features and advantages of this inventionare set forth in the remainder of the specification and are shown in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a fuel cell assembly according to a firstembodiment.

FIG. 2 is a sectional view of a fuel cell assembly according to a secondembodiment.

FIG. 3 is a sectional view of a fuel cell assembly according to a thirdembodiment.

FIG. 4 is a sectional view of a fuel cell assembly according to a fourthembodiment.

FIG. 5 is a sectional view of a fuel cell assembly according to a fifthembodiment.

FIG. 6 is a sectional view of a fuel cell assembly according to a sixthembodiment.

FIG. 7 is a sectional view of a fuel cell assembly according to aseventh embodiment.

FIG. 8 is a sectional view of a fuel cell assembly according to aneighth embodiment.

FIG. 9 is a schematic diagram of a fuel cell system according to a ninthembodiment.

FIG. 10 is a schematic diagram of a fuel cell system according to atenth embodiment.

FIG. 11 is a schematic diagram of a fuel cell system according to aneleventh embodiment.

FIG. 12 is a flowchart describing an example of a startup controlroutine performed by a controller according to the tenth embodiment.

FIG. 13 is a flowchart describing an example of a startup controlroutine performed by a controller according to the eleventh embodiment.

DESCRIPTION OF TIE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, a first embodiment will bedescribed. A fuel cell assembly 1 comprises a fuel cell stack 2 formedby laminating a plurality of cells and plus and minus current extractionsections 3 sandwiching the fuel cell stack 2 with respect to thedirection of lamination of the fuel cell stack 2. The cell includes amembrane electrode assembly (MEA) and a separator which forms one ormore passages allowing the supply of oxygen or hydrogen to the anode orthe cathode. The MEA comprises a polymer electrolyte membrane, a gasdiffusion electrode acting as a cathode and a gas diffusion electrodeacting as an anode.

The current extraction section 3 has an integrated structure in whichthe current extraction plate and the end plate are integrated. The endplate presses uniformly the cells of the fuel cell stack 2 to bind themin the direction of lamination. The current extraction plate extractscurrent produced in the fuel cell assembly 1 to the outside. The currentextraction section 3 incorporates both the function of the currentextraction plate and the end plate. The end plate may be realized by aplate connected with the connector of the cooling medium passage or thegas distribution passage and it may function as an electricallyinsulating member.

As shown in some embodiments described hereafter, when the end plate andthe current extraction plate are provided as separate units in contrastto this embodiment, it is possible to improve the thermal insulation ofthe fuel cell assembly 1 under normal operating conditions after startupsince materials having different coefficients of thermal conductivityare used in the current extraction plate and the end plate. Moreprecisely, the end plate may be formed from a material which has a lowercoefficient of thermal conductivity than that of the current extractionsection.

One side of the current extraction section 3 has an indented section 3 awhich acts as a passage allowing flow of a heating medium (for example agas such as air or hydrogen). The open side of the indented section 3 ais disposed facing the fuel cell stack 2. Rather than a gas, the heatingmedium may comprise a liquid such as cooling water used for cooling thefuel cell stack 2 under normal operating conditions.

The flow of gas in the current extraction section 3 reduces the overallheat capacity of the current extraction section 3. Further the thermalinsulation characteristics of the gas interfere with the transmission ofheat from the laminated cell 2 to the current extraction section 3. Inthis manner, heat of the end cell can be prevented from being deprivedby the current extraction section 3 during cold startup at a temperaturebelow freezing. Furthermore it is possible to rapidly increase thetemperature of the end cell positioned on the end of the laminated cell2. Furthermore it is possible to improve the power generation conditionsof the fuel cell stack during startup at a temperature below freezing.

Referring to FIG. 2, the fuel cell assembly 1 according to a secondembodiment will be described. The structure of the current extractionsection is different to that described in the first embodiment.

The current extraction section 4 has a passage 4 a (or open cavity)allowing gas flow inside the current extraction section 4. This type ofstructure ensures the rigidity of the current extraction section inaddition to obtaining the effect of the first embodiment. Furthermorethe structure effectively fixes the fuel cell stack 2 and improves theair-tight characteristics of the passage 4 a.

Referring to FIG. 3, the structure of the fuel cell assembly 1 accordingto a third embodiment will be described. The current extraction section5 comprises a current extraction plate 5 a and an end plate 5 b. Thecurrent extraction section and the end plate are provided as separatecomponents. Thus it is possible to improve the thermal insulation of thefuel cell assembly 1 by forming the end plate 5 b with a material whichhas a lower coefficient of thermal conductivity than the material usedin the current extraction plate 5 a. One side of the current extractionplate 5 a is fixed to the end face of the fuel cell stack 2 with respectto the direction of lamination. An indented section 5 c is formed on theother side of the current extraction plate 5 a to allow gas flow. Theend plate 5 b seals the opening of the indented section 5 c. In thismanner, gas flow is enabled in the indented section 5 c. Therefore thisstructure makes it possible to form a passage for gas flow in a simplemanner.

Referring to FIG. 4, the fuel cell assembly 1 according to a fourthembodiment will be described. The current extraction section 6 comprisesa current extraction plate 6 a and an end plate 6 b. The currentextraction plate 6 a is formed as a flat plate and is affixed to thefuel cell stack 2. The indented section 6 c is adapted to allow gas flowon one side of the end plate 6 b. The current extraction plate 6 a sealsthe opening of the indented section 6 c. Thus gas flow can be realizedin the indented section 6 c. Thus this structure realizes the sameeffect as that obtained by the third embodiment.

Referring to FIG. 5, a fuel cell assembly 1 according to a fifthembodiment will be described. The current extraction section 7 comprisesa current extraction plate 7 a and an end plate 7 b. Both the currentextraction plate 7 a and an end plate 7 b have an indented section onone side. The openings of both indented sections face one another toform the space 7 c. Gas flows into the space 7 c formed by the openings.This structure realizes the same effect as that obtained by the thirdand fourth embodiments.

Referring to FIG. 6, a fuel cell assembly 1 according to a sixthembodiment will be described. The current extraction section 8 comprisesa current extraction plate 8 a and an end plate 8 b. The currentextraction plate 8 a comprises a passage 8 c (or open cavity) allowinggas flow therein. The end plate 8 b is a flat plate. Since the currentextraction plate 8 a has a passage 8 c therein, the same effect as thesecond embodiment is obtained. The current extraction section 8 furthercomprises an end plate 8 b. It is possible to improve thermal insulationof the fuel cell assembly 1 if the end plate 8 b is formed from amaterial which has a lower coefficient of thermal conductivity than thematerial for forming the current extraction plate 8 a. Furthermore it ispossible to improve thermal insulation by using an insulating materialas the material for forming the end plate 8 b.

Referring to FIG. 7, a fuel cell assembly 1 according a seventhembodiment will be described. A current extraction section 9 comprises acurrent extraction plate 9 a and an end plate 9 b. The currentextraction plate 9 a is a flat plate. The end plate 9 b comprises apassage 9 c allowing gas flow therein. This structure realizes the sameeffect as the sixth embodiment.

Referring to FIG. 8, a fuel cell assembly 1 according an eighthembodiment will be described. A current extraction section 10 comprisesa current extraction plate 10 a and an end plate 10 b. The currentextraction plate 10 a and the end plate 10 b comprise passages 10 c, 10d allowing gas flow therein. This structure realizes the same effect asthe sixth and seventh embodiments.

As shown by the third through the eighth embodiments, the heat capacityof the current extraction section is reduced in the same manner as thefirst and the second embodiments by allowing gas flow in the currentextraction section which comprises a current extraction plate and an endplate. In this manner, during startup at a temperature below freezing,it is possible to avoid heat being taken by the current extractionsection and to promote temperature increase in the end cell. Furthermoreit is possible to improve the power generation conditions of the fuelcell stack during startup at a temperature below freezing.

An enclosed cavity which has any type of gas-tight structure andconfines gas therein may be used instead of any passage shown in thefirst to eighth embodiments. It is preferred that the gas is sealed inthe enclosed cavity at a reduced pressure.

Referring to FIG. 9, a ninth embodiment will be described. Thisembodiment relates to a fuel cell system. Although the fuel cellassembly 1 has the same structure as that described with reference tothe second embodiment, any structure in the embodiments above willsuffice.

An anode intake pipe 20 supplies hydrogen to the anode of each cell ofthe fuel cell stack 2. The anode outlet pipe 21 discharges hydrogeneffluent from each cell of the fuel cell stack 2 to the externalatmosphere. The cathode inlet pipe 22 supplies air or anoxygen-containing gas to the cathode of each cell. The cathode outletpipe 23 discharges effluent air or discharge gas discharged from eachcell to the external atmosphere.

A humidifier 24 functioning as a heating device is disposed respectivelyin the anode intake pipe 20 and the cathode intake pipe 22. Air andhydrogen is supplied to the cell after being heated to a predeterminedtemperature by the humidifier 24. A bypass pipe 26 branches at abranching point 25 downstream of the humidifier 24 of the cathode inletpipe 22. The bypass pipe 26 is connected to the upstream currentextraction section 4 b which is disposed upstream from the downstreamcurrent extraction section 4 c. A control valve 27 is disposeddownstream of the branching point 25 of the cathode inlet pipe 22. Acontrol valve 28 is disposed in the bypass pipe 26 between the branchingpoint 25 and the upstream current extraction section 4 b. The airsupplied through the bypass pipe 26 passes through the passage 4 a ofthe upstream current extraction section 4 b and is supplied to thedownstream current extraction section 4 c after passing through a pipe49. Air discharged from the downstream current extraction section 4 c isdischarged to the external atmosphere.

The control valves 27, 28 are opened and closed by a controller 60. Thehumidifier 24 is also controlled by the controller 60. The controller 60comprises a microcomputer provided with a central processing unit (CPU)executing programs, a read-only memory (ROM) storing data or programs, arandom access memory (RAM) temporarily storing obtained data as well ascalculation results from the CPU and an input/output interface (I/Ointerface).

In order to increase the temperature of the current extraction section4, air heated by the humidifier 24 is supplied to the current extractionsection 4 through a control valve 28. In addition, heated air passingthrough the control valve 27 is supplied to the cells. Furthermorehydrogen is supplied to the cells and power generation operations arecommenced in each cell. Thus when startup is performed below freezing,the humidifier 24 heats the current extraction section 4 by allowingheated air to flow through the current extraction section 4. Radiationof heat from the current extraction section 4 promotes temperatureincrease in the end cell which tends to display a low power generationefficiency at low temperatures. The temperature increase in the end cellmakes the overall temperature of the fuel cell stack 2 uniform andimproves power generation efficiency. Before power generation operationsare commenced in the fuel cells, heated air may be supplied to thecurrent extraction section 4 by closing the control valve 27 and openingthe control valve 28 in order to increase the temperature of the endcell before power generation.

It is stressed that the heating device is not limited to the humidifier24 but may be a compressor, a combustor or a gas heater. Apart from hightemperature gas, the current extraction section may be heated byallowing a high-temperature liquid to flow in the passage.

When the fuel cell stack is operating under normal conditions afterstartup, sufficient air is supplied to the fuel cell stack 2 by closingthe control valve 28 since it is not necessary to heat the end cell.Furthermore when the fuel cell stack has reached a higher temperaturethan the temperature of the supplied air, the temperature of the fuelcell stack may be reduced by opening the control valve 28 in order tolimit the air supplied to the fuel cell stack 2.

Referring to FIG. 10, a fuel cell system according to a tenth embodimentwill be described. When compared to the fuel cell according to the ninthembodiment, the tenth embodiment omits the bypass pipe 26 and thecontrol valves 27, 28. A control valve 29 is disposed in the anodeintake pipe 20 upstream of the humidifier 24 and a control valve 30 isdisposed in the cathode intake pipe 22 upstream of the humidifier 24. Agas pipe 32 branches from the intake pipes 20, 22 upstream of thecontrol valves 29, 30. The gas pipe 32 is connected to the two currentextraction sections 4 b, 4 c positioned on both ends of the fuel cellstack 2. A gaseous mixture of air and hydrogen is supplied to thecurrent extraction section 4. The gaseous mixture is discharged to theexternal atmosphere after passing through the current extraction section4. A control valves 33, 34 are disposed in the gas pipe 32 whichbranches from each intake pipe 20, 22. The control valve 33 regulatesthe flow of hydrogen supplied to the current extraction section 4. Thecontrol valve 34 regulates the flow of air supplied to the currentextraction section 4. The control valves 29, 30, 33, 34 are opened andclosed by the controller 60.

A catalyst 90 acting as a combustion means is applied to the wall faceof the passage 4 a of the current extraction section 4. The heat ofcombustion of the gaseous mixture is produced by catalytic reactions inthe passage 4 a as a result of supplying a gaseous mixture of hydrogenand oxygen to the passage 4 a. The end cell is effectively heated bytransmitted heat from the current extraction section 4 which directlygenerates heat by the catalyst 90. In the tenth embodiment, the heatingdevice which heats the passage 4 a of the current extraction section 4comprises a gas pipe 32 supplying the gaseous mixture of air andhydrogen to the current extraction section 4 and a catalyst 90 providedin the passage 4 a of the current extraction section 4.

Referring to FIG. 12, an example of a startup control routine performedby the controller 60 according to the tenth embodiment will bedescribed. Firstly in a step S1, the control valve 34 is opened beforepower generation operations and air is supplied at a flow rate of 10liters per minute only to the current extraction section 4. Then in astep S2, a first waiting time is set. The first waiting time ispredetermined as a time during which the temperature of the catalyst 90applied to the passage 4 a is increased to higher than a predeterminedtemperature (for example, to the catalyst activation temperature). Thefirst waiting temperature may be predetermined as the time required forthe flow rate of air to stabilize. After the first waiting time haselapsed, in a step S3, the control valve 33 is opened and hydrogen issupplied to the pipe 32 at a rate of 0.4 liters per minute. In thismanner, a gaseous mixture of hydrogen and air passes through the passage4 a of the current extraction section 4 from the pipe 32.

The gaseous mixture of hydrogen and air is combusted by the catalyst 90in the passage 4 a The heat produced as a result of the catalyticcombustion heats the end cell. In a step S4, a second waiting time isset. The second waiting time is predetermined as a time required for thetemperature of the end cell to increase to a temperature 5 degrees C. to10 degrees C. higher than that of the other cells. In a step S5, thecontrol valves 29, 30 are opened. Air and hydrogen are supplied to thefuel cell stack 2. Consequently power generation is commenced in thefuel cell stack 2. This type of control allows the end cell to be heatedby increasing the temperature of the current extraction section usingthe gaseous mixture of air and hydrogen which should have been suppliedto the fuel cell stack 2.

During normal operation, the control valve 33 is closed and only thecontrol valve 34 is opened. Consequently air from the gas pipe 32effectively removes moisture produced by catalytic reactions in thepassage 4 a. This prevents moisture in the passage 4 a from freezing attemperatures below zero and improves the startup performance at atemperature below freezing.

When the operation of the fuel cell system is stopped, the supply of thegaseous mixture of hydrogen and air may be continued to the currentextraction section 4. Even when the temperature of the externalatmosphere falls below zero while operation is stopped, it is possibleto avoid the temperature of the fuel cell stack 2 from falling belowfreezing point by supplying the gaseous mixture. In this case, thestartup control routine described above is not required.

Instead of the startup control routine above, it is possible to furtherimprove startup performance by opening the control valves 29, 30, 33, 34simultaneously with the commencement of a startup operation at atemperature below freezing.

Referring to FIG. 11, an eleventh embodiment will be described. The fuelcell system comprises an anode intake pipe 20, an anode outlet pipe 21,a cathode intake pipe 22, a cathode outlet pipe 23 and two humidifiers24. A control valve 29, 30 is disposed in each intake pipe upstream ofthe humidifier 24. A pipe 35 branching from the cathode intake pipe 22upstream of the control valve 30 and a pipe 36 branching from the anodeoutlet pipe 21 joins together into the confluent-flow pipe 37. Theconfluent-flow pipe 37 branches again into a pipe 38 and a pipe 39. Thepipes 38, 39 are respectively connected to the current extractionsection 4 b, 4 c disposed on both ends of the fuel cell stack 2. Acontrol valve 40 is disposed in the pipe 35 and a control valve 41 isdisposed in the pipe 36. The control valves 40, 41 are opened and closedby the controller 60.

Referring to FIG. 13, an example of a startup control routine executedby the controller 60 according to an eleventh embodiment will bedescribed. Firstly in a step S11, the control valves 29, 30, 40 areopened so that air and hydrogen are supplied to the fuel cell stack 2 inorder to commence power generation. Furthermore air is supplied to thecurrent extraction section 4 through the pipes 35, 37, 38, 39. In a stepS12, a third waiting time is set. For example, the third waiting time isthe time until a stable air flow rate of 10 liters per minute isreached. In a step S13, the control valve 41 is opened. In this manner,hydrogen effluent from the anode of the cells in the fuel cell stack 2is supplied from the pipe 36 to the pipe 37. Then, the gaseous mixtureof air and hydrogen effluent is supplied to the current extractionsection 4. The supply rate of hydrogen is of the order of 0.4 liters perminute. The end cell is heated by supplying a gaseous mixture to thecurrent extraction section 4 which is combusted by the catalyst 90applied to the passage 4 a of the current extraction section 4. Inaddition to the effect obtained by the tenth embodiment, the eleventhembodiment allows hydrogen effluent to be used effectively.

During normal operation, moisture produced by the current extractionsection 4 is discharged to the external atmosphere by closing thecontrol valve 41 and holding the control valve 40 in the open position.Thus it is possible to prevent deterioration in the catalytic reactionof the catalyst 90 applied to the passage 4 a as a result of moisture inthe passage 4 a freezing at a temperature below freezing.

In the fuel cell system according to the tenth and eleventh embodiments,an ignition device (combustion means) such as a spark plug forcombustion of the gaseous mixture may be provided in order to combustthe air and hydrogen. Thus the end cell may be heated by the supply ofcombustion gas to the current extraction section 4. Consequently, inthis case, the catalyst 90 may not be applied to the passage 4 a of thecurrent extraction section 4. Thus it is possible to rapidly increasethe temperature of the current extraction section 4 by providing theignition device.

The entire contents of Japanese Patent Application P2003-123673 (filedApr. 28, 2003) are incorporated herein by reference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art, inlight of the above teachings. The scope of the invention is defined withreference to the following claims.

1. A fuel cell assembly comprising: a fuel cell stack formed bylaminating a plurality of cells; plus and minus current extractionsections, the current extraction sections extracting current generatedby the fuel cell stack and sandwiching the fuel cell stack with respectto the direction of lamination, each current extraction sectioncomprising a current extraction plate which is fixed to an end cellpositioned on an end of the fuel cell stack so as to extract thegenerated current, and an end plate for uniformly binding the cells ofthe fuel cell stack; and a passage allowing flow of oxygen gas andhydrogen gas during startup of the fuel cell stack at a temperaturebelow freezing, provided for at least one of the current extractionplate and the end plate, wherein a catalyst for combusting the gas isapplied to a wall face of the passage and wherein the passage passesonly the current extraction sections and does not supply the fuel cellstack with the oxygen gas and hydrogen gas.
 2. The fuel cell assembly asdefined in claim 1, wherein the passage for the gas is formed betweenthe current extraction plate and the end plate.
 3. The fuel cellassembly as defined in claim 1, wherein the passage is formed inside atleast one of the current extraction plate and the end plate.
 4. A fuelcell system comprising: a fuel cell assembly comprising; a fuel cellstack formed by laminating a plurality of cells; plus and minus currentextraction sections, the current extraction sections extracting currentgenerated by the fuel cell stack and sandwiching the fuel cell stackwith respect to the direction of lamination, each current extractionsection comprising a current extraction plate which is fixed to an endcell positioned on an end of the fuel cell stack so as to extract thegenerated current, and an end plate for uniformly binding the cells ofthe fuel cell stack; a passage allowing flow of a fluid during startupof the fuel cell stack at a temperature below freezing, provided for atleast one of the current extraction plate and the end plate, wherein thepassage passes only the current extraction section and does not supplythe fuel cell stack with the fluid; a control valve which is open tosupply the fluid to the passage during startup of the fuel cell stackand which is closed to stop supplying the fluid to the passage undernormal conditions of the fuel cell stack after the startup; and aheating device for heating the passage for the fluid.
 5. The fuel cellsystem according to claim 4, wherein the fluid is combustible and theheating device comprises a catalyst applied to the passage in order tocombust the fluid.
 6. The fuel cell system according to claim 4, whereinthe heating device heats the fluid and supplies the heated fluid to thepassage.
 7. The fuel cell system according to claim 4, wherein the fluidis combustible and the heating device comprises an ignition device forcombusting the fluid.
 8. The fuel cell system according to claim 4,wherein the heating device heats at least one of the current extractionsections when the fuel cell stack is started up.
 9. The fuel cell systemaccording to claim 8, wherein the heating device comprises means forcombusting cathode gas for the fuel cell stack and the heating deviceheats at least one of the current extraction sections using the heat ofcombustion.
 10. The fuel cell system according to claim 8, wherein theheating device comprises means for combusting a gaseous mixture ofcathode gas and anode gas for the fuel cell stack and the heating deviceheats at least one of the current extraction sections using the heat ofcombustion.
 11. The fuel cell system according to claim 10, wherein theanode gas is an anode gas discharged from the fuel cell stack.
 12. Thefuel cell system according to claim 8, wherein the heating devicecomprises means for supplying anode gas for the fuel cell stack to thecurrent extraction sections after supplying cathode gas for the fuelcell stack to the current extraction sections and means for combustingthe gaseous mixture of anode gas and cathode gas.
 13. The fuel cellsystem according to claim 12, wherein the anode gas is an anode gasdischarged from the fuel cell stack.
 14. The fuel cell system accordingto claim 4, wherein the passage for the fluid is formed between thecurrent extraction plate and the end plate.
 15. The fuel cell systemaccording to claim 4, wherein the passage is formed in at least one ofthe current extraction plate and the end plate.
 16. A fuel cell assemblycomprising: a fuel cell stack formed by laminating a plurality of cells;plus and minus current extraction sections, the current extractionsections extracting current generated by the fuel cell stack andsandwiching the fuel cell stack with respect to the direction oflamination, each current extraction section comprising a currentextraction plate which is fixed to an end cell positioned on an end ofthe fuel cell stack so as to extract the generated current, and an endplate for uniformly binding the cells of the fuel cell stack; and anenclosed cavity for confining gas therein formed in at least one of thecurrent extraction sections, the gas being sealed in the enclosed cavityat reduced pressure; wherein the end plate is formed from a materialwhich has a lower coefficient of thermal conductivity than a materialfor forming the current extraction plate.
 17. The fuel cell assembly asdefined in claim 16, wherein the enclosed cavity is formed between thecurrent extraction plate and the end plate.
 18. The fuel cell assemblyas defined in claim 16, wherein the enclosed cavity is formed inside atleast one of the current extraction plate and the end plate.